St. John's wort (Hypericum perforatum) is a flowering shrub native to Europe, parts of Asia and Africa, and the Western United States. It’s named after St. John the Baptist since it’s usually in full bloom by June 24, and the word “wort” is an old English word for plant.

The flowers and leaves of St. John's wort contain dozens of biologically active substances, but hyperforin and hypericin have the greatest activity. These two compounds may influence a number of neurotransmitters thought to play a role in maintaining healthy brain function. Neurotransmitters, including chemicals such as serotonin and dopamine, are responsible for transmitting messages between neurons (i.e., nerve cells). Today, it remains a popular herb used to support a positive mood and emotional well-being.

Dried St. John's wort leaves can be used to make tea. It’s a good source of flavonoids, phenolic acids, glycosides, rutin, tannins, resins and essential oils. It’s also available as a supplement in capsules, tablets, liquids and topical preparations.

St. John's wort interacts with many medications (including certain antidepressants, birth control pills, and blood-thinning drugs) and can cause serious side effects. Don't use St. John's wort if you take prescription medications.